Sounds like you need a third related table for logging the days worked.
Is this a new database or are you trying to get this to work for existing data?
If this is from existing data, how did you record instances where a single contact worked more than one day?
I started this from the "Events" starter solution in FMPA 11. The tables were close enough to allow me to make it work,
The tables are Registration, Contacts, Booths.
There is a portal that gets its data from the Registration Contact ID table, Booths days info is stored here.
This does not change my suggestion that you add a one record for each time a given contact works in a given booth.
If this is your basic relationship:
you can either add a date field in Registration and create one registration record for each time a contact will work in a booth or you can link a third table to Registration by __pkRegistrationID (An auto-entered serial number to uniquely identify each record in registration) to use for that purpose.